1. Field
This disclosure relates generally to power amplifiers, and more specifically, to a power amplifier having a single input RF chain that is directly coupled with a plurality of parallel output RF chains.
2. Background
Modern mobile communication devices are designed with a requirement that they function correctly in as many mobile communication networks as possible. These networks may or may not be geographically distinct and may be governed by a plurality of modulation standards and operate in a plurality of frequency bands. One way to satisfy this requirement is for the mobile communication device to include multiple RF signal paths, wherein each RF path is dedicated to the support of a given communication standard and/or frequency band.
Market pressure for miniaturization and cost reduction of mobile communication devices is driving the RF architecture towards an approach that minimizes the number of independent RF signal paths. The constant rise of computing power and digital signal processing have naturally allowed for the merger of multiple modulation standards within a single transceiver baseband chip. Similarly, improvements in the performance of CMOS devices provides for the ability to design RF transceivers capable of operating in multiple frequency bands. However, maintaining a single RF signal path from the output of the single transceiver to the single antenna cannot yet be achieved because efficient RF Power Amplifiers (PAs) require accurately tuned, narrow band, high quality matching networks, followed by different bandpass filters for the various frequency bands that need to be supported by the communication device.
FIG. 1 shows multiple PAs 110, 120, 130 driven by a single transceiver by means of a single-pole multi-throw (SPMT) switch 140. The need to replicate the entire RF signal path for each frequency band, starting from the output of the transceiver and continuing to the antenna input, is not conducive to the achievement of significant reduction in cost and physical dimensions.
FIG. 2 shows a single integrated PA 210 followed by an SPMT switch 230 coupled to the output of the PA (RFo). The PA 210 includes a stage-3 power driver 212, a stage-3 match circuit 214, a stage-2 power driver 216, a stage-2 match circuit 218, a stage-1 power driver 220, and a stage-1 match circuit 222. However, a PA, using a single transformation network, cannot produce an efficient RF amplification at multiple frequencies because of the combination of the transformation network's narrow-band characteristic and carefully-adjusted reactive elements. One solution is to place independent corrective reactive networks 240, 250, 260 following the SPMT switch 230, one network 240, 250, or 260 for each separate frequency band RF signal path. Thus, when selected, each frequency band RF path operates as a PA terminated on a two-stage transformation network, wherein the first stage 270 is shared among all bands and the second stage 280 is uniquely associated with the currently selected band. While this approach achieves the goal of leveraging a single PA among many frequency bands, it has several disadvantages. One of them is that the switch implementation requires a special high-voltage semiconductor process that delivers transistors capable of tolerating such voltages (e.g., RFo).